It will be nice to have this feature realized in Collector for ArcGIS.
This is a MUST-HAVE feature for any assessment scenario: the locations of the subject being assessed are generated in a separate process by professionals, these are authoritative data which are strictly protected and not allowed to be changed by field workers, who are no experts in collecting spatial data but experts in their own business area like utility services, disaster relief, damage assessment of all sorts. The assessment forms are normally organised as the related tables for the feature layers (properties, business, pipelines, valves etc.) on the map.
I know we can disable editing for the feature layer in the web map to prevent it from being edited by the field workers. but this will disable editing for the attribute table of the feature layer, and in the attribute table we have some fields holding the information for the process of the assessment, and according to these information to symbolize our data. so we need "update attribute only" setting for the feature layer to make dynamic symbolization possible.
Currently, in Collector, if we select "update attribute only" for the feature layer, all the related tables are read-only and we can only view the records in them. This is ... not very helpful.
We might be able to workaround this in some cases, but enable editing for related table while the feature server is "Update Attributes Only" should be the most straightforward solution.